1. Field of the Invention
The invention concerns a medullary nail (sometimes referred to as a marrow nail) for bone distraction with an electric motor drive arranged in its interior, preferably in its interior in the area of its drive-end, with the electric motor drive being connected to a reception antenna for feeding energy via an electrical connection.
2. Description of the Background Art
From DE 39 21 972 C2 and DE 197 00 225 A1, we are familiar with the utilization of a medullary nail that can be inserted into the bone medullary area as an active implant for the purpose of simultaneous stabilization and distraction of surgically separated hollow bones, particularly in order to extend bones and bridge bone defects. DE 39 21 972 C2 mentions mechanical, pneumatic, hydraulic, electric, electromagnetic and piezo-electric drives in general as power sources that are located in the medullary nail""s interior.
According to DE 197 00 225 A1, the planetary roller spindle system known from EP 0 320 621 is considered beneficial.
In both drive systems energy is fed from the outside through the skin via an antenna, which is connected with the drive in the medullary nail""s interior via a cable.
Furthermore we know of a distraction device which incorporates not only the drive, but also all energy reserves and controls in a capsule so that the system works completely autonomously and must be accessed from the outside only for programming purposes.
The cable connection between the antenna and the drive system represents a highly stressed component. The medullary nail on the femur (thigh bone) is inserted between the greater trochanter and the neck of the femur. This is also where the cable exits and leads to the antenna, which is usually located subcutaneously. With every movement of the leg, the cable exit area performs a circular segment motion with the turning center of the hip joint, which exposes the cable at the exit area out of the bone to a bending stress with very small bending radius, in particular since ossifications also occur in this area on a regular basis. Even when employing highly flexible cables, such as those common in pacemakers, durability cannot be guaranteed with certainty. Problems also arise upon removal of the cable later on, which is sheathed in the tissue by a delicate cover of connective tissue. In case the cable breaks or is damaged during surgery, unsterile material can come in contact with body fluids.
According to DE 39 21 972 C2 (FIG. 1), the distraction device cannot be employed on the tibia since in its proximity a bend in the medulary nail is required for anatomical reasons to ensure that the medullary nail is not pulled into the bone by the distraction process.
In this case, the drive system from DE 197 00 225 A1 (FIG. 2) would be suitable because the drive is located distally of the bend. However even in this case routing of the cable, which leaves the bone immediately before the crucial ligament and runs through the knee cap to the subcutaneously located antenna, is problematic.
If we were to design the drive for the medullary nail as described in DE 39 21 972 D2 in such a way that it would be located distally, then it is true that its function would be ensured since the medullary nail will be able to run proximally. The cable connection to the outside, however, would have to be routed through the nail or next to the nail on its outside, which would be very complex from a technical point of view.
On the version mentioned above where not only the drive, but also all energy reserves and controls are encapsulated, the cable routing problem has been eliminated through the complete integration of all components into the medullary nail""s interior. Energy resources, however, are limited and the system is prone to failures; furthermore, there is the risk that the system may become independent.
In summary, this shows that considerable disadvantages arise from known drive systems, not only with a cable connection routed freely through body tissue between the components in the nail""s interior and the antenna, which is generally located subcutaneously, but also with complete implantation of all components, including the energy supply, into the medullary nail""s interior.
The object of the invention comprises designing medullary nails of the kind described above in such a way that an energy feeding system is guaranteed both on the femur and the tibiaxe2x80x94while maintaining distraction under tension in accordance with DE 39 21 972 C2 or while maintaining the telescope mechanism in accordance with DE 197 00 225 A1xe2x80x94which avoids both the disadvantages of a complete integration of energy reserves into the encapsulated system and those of a cable connection to a subcutaneously located reception system.
Based on medullary nails of the kind described above, this object is arrived at by locating the reception antenna and electrical connection either entirely in the interior of the medullary nail and equipping the medullary nail with an orifice that faces the reception antenna and permits the feeding of energy, or immediately on the front so that energetic shielding cannot occur from the metal of the medullary nail.
On the invented medullary nail, all cable connections outside the medullary nail are eliminated. At the same time, the required feeding energy system is made possible with the help of a high frequency transmitter, which can transmit the required energy without difficulty when positioned in appropriate proximity. This design always makes the desired energy resources, which are required for the drive, available without having to install them as such within the medullary nail. The orifice can be closed off in a wall-like manner with a material that allows the feeding of energy so that the medullary nail has a consistently even outline.
The orifice can be located in the wall of the medullary nail. If in this version the drive, the reception antenna and its electrical connection, usually a cable or plug-type connector, were arranged in the same housing, then it would be inserted into the medullary nail""s interior in such a way that one orifice of the joint housing facing the reception antenna would be opposite the orifice in the wall of the medullary nail. This enables pre-assembly of the drive, reception antenna and electrical connection in the joint housing without this joint housing representing a shield that would impair the energy feeding process. The orifice in the joint housing can certainly also be closed off by a material that permits the feeding of energy so that the joint housing has a flush outer wall or is connected with the material, which permits the feeding of energy, in the orifice of the medullary nail""s wall without joints. The joint housing can consist of metal.
Generally, an epoxy resin or silicone rubber that is tolerated by the body is utilized as the material that allows the feeding of energy.
At least the reception antenna, and usually its electrical connection as well, can be enclosed by a casing-like encapsulation made of material that allows the feeding of energy, with the possibility of the encapsulation being firmly connected to the electric motor drive and inserted into the medullary nail""s interior with or without drive.
In order to enable true alignment of the reception antenna and the orifices, adjusting elements can be provided for on the medullary nail and the housing or the encapsulation, e.g. in a recess extending distally from the tip of the medullary nail and a lug protruding radially from the housing or encapsulation. Similarly, the adjusting elements can consist of the orifice in the wall of the medullary nail and a neck that protrudes from the circumferential area of the encapsulation in alignment with the reception antenna and snaps into the orifice in a form-fit way, if this neck, like the encapsulation, is made of elastic silicone rubber.
In a special design the orifice can extend distally in axial direction over the entire circumferential area of the medullary nail, starting from its tip. In this case the encapsulation protrudes proximally beyond the material that allows the feeding of energy and axially beyond the medullary nail, and forms a cap that encloses the reception antenna.
In all cases that have been mentioned, it is possible to attach a suitable tool to the medullary nail on the front in order to be able to place the medullary nail into the bone and remove it again.